1. Field of the Invention
The present invention relates generally to apparatus and methods for determining whether the continuity of the optical coupling between optical fibers is acceptable, and more particularly, to apparatus and methods for verifying an acceptable splice termination between a field optical fiber and a stub optical fiber in a fiber optic splice connector.
2. Technical Background
Optical fibers are useful in a wide variety of applications, including the telecommunications industry in which optical fibers are employed for voice, data and video transmission. Due, at least in part, to the extremely wide bandwidth and the low noise operation provided by optical fibers, the variety of applications in which optical fibers are being used is continuing to increase. For example, optical fibers no longer serve merely as a medium for long distance signal transmission, but are being increasingly routed directly to the home, and in some instances, directly to a desk or other work location. With the ever increasing and varied use of optical fibers, apparatus and methods have been developed for coupling optical fibers to one another outside the controlled environment of a factory setting, commonly referred to as “field installation” or “in the field,” such as in a telephone central office, in an office building, and in various types of outside plant terminals. However, in order to efficiently couple the optical signals transmitted by the fibers, a fiber optic connector must not significantly attenuate, reflect or otherwise alter the optical signals. In addition, fiber optic connectors for coupling optical fibers must be relatively rugged and adapted to be connected and disconnected a number of times in order to accommodate changes in the optical transmission path that may occur over time.
Although fiber optic connectors can generally be most efficiently and reliably mounted upon the end portion of an optical fiber in a factory setting during the production of a fiber optic cable assembly, many fiber optic connectors must be mounted upon the end portion of an optical fiber in the field in order to minimize cable lengths and to optimize cable management and routing. As such, a number of fiber optic connectors have been developed specifically to facilitate field installation. One advantageous type of fiber optic connector that is designed specifically to facilitate field installation is the UNICAM® family of field-installable fiber optic connectors available from Corning Cable Systems LLC of Hickory, N.C. Although the UNICAM® family of field-installable connectors includes a number of common features including a common termination technique (i.e., mechanical splice), the UNICAM® family also offers several different styles of connectors, including mechanical splice connectors adapted to be mounted upon a single optical fiber and mechanical splice connectors adapted to be mounted upon two or more optical fibers. Regardless, each such field-installable fiber optic connector requires a method of determining whether the continuity of the optical coupling between the fiber optic connector and a field optical fiber mounted upon the fiber optic connector is acceptable. As used herein, this process is generally referred to as “verifying an acceptable splice termination.” Typically, a splice termination is acceptable when a variable related to the optical performance of the connector, such as insertion loss or reflectance, is within a prescribed limit or threshold value. In a particular example, the splice termination is acceptable when the insertion loss of the connector as indicated by an optical power meter or Optical Time Domain Reflectometer (OTDR) is less than a predetermined value.
A conventional field-installable fiber optic connector 10 is illustrated in FIGS. 1A and 1B. By way of example, the fiber optic connector 10 shown in FIGS. 1A and 1B is a field-installable SC style UNICAM® mechanical splice connector developed by Corning Cable Systems LLC. However, the apparatus and methods described herein are applicable to verifying the continuity of the optical coupling between any pair of interconnected optical fibers, and more particularly, between a field optical fiber and an optical fiber of any fiber optic splice connector, including a single fiber or multifiber fusion splice or mechanical splice connector. Examples of typical single fiber mechanical splice connectors are provided in U.S. Pat. Nos. 4,755,018; 4,923,274; 5,040,867; and 5,394,496. Examples of typical multifiber mechanical splice connectors are provided in U.S. Pat. Nos. 6,173,097; 6,379,054; 6,439,780; and 6,816,661. As shown herein, the mechanical splice connector 10 includes a ferrule 12 defining a lengthwise, longitudinal bore for receiving a stub optical fiber 14. The stub optical fiber 14 is preferably sized such that one end extends outwardly beyond the rear end 13 of the ferrule 12. The mechanical splice connector 10 also includes a pair of opposed splice components 17, 18, at least one of which defines a lengthwise, longitudinal groove for receiving and aligning the end portion of the stub optical fiber 14 and an end portion of a field optical fiber 15 upon which the mechanical splice connector 10 is to be mounted.
In order to mount the connector 10 upon the field optical fiber 15, the splice components 17, 18 are positioned proximate the rear end 13 of the ferrule 12 such that the end portion of the stub optical fiber 14 extending rearwardly from the ferrule is disposed within the groove defined by the splice components. Thereafter, the end portion of the field optical fiber 15 can be inserted into the groove defined by the splice components 17, 18. By advancing the field optical fiber 15 into the groove defined by the splice components 17, 18, the end portions of the stub optical fiber 14 and the field optical fiber 15 make physical contact and establish an optical connection, or coupling, between the field optical fiber and the stub optical fiber. The splice termination of the fiber optic connector 10 is completed as illustrated in FIG. 1B by actuating a cam member 20 to bias the splice components 17, 18 together, and thereby secure the end portions of the stub optical fiber 14 and the field optical fiber 15 within the groove defined by the splice components. If the continuity of the optical coupling between the field optical fiber 15 and the stub optical fiber 14 is acceptable (e.g., the insertion loss is less than a prescribed value and/or the reflectance is greater than a prescribed value), the cable assembly can be completed, for example by strain relieving the buffer 25 of the field optical fiber to the splice connector 10 in a known manner.
Installation tools have also been developed to facilitate the splice termination of one or more optical fibers to a fiber optic connector, and particularly, to enable the splice termination of one or more field optical fiber to a mechanical splice connector. Examples of typical installation tools for facilitating the connectorization of one or more optical fibers to a mechanical splice connector in the field are described in U.S. Pat. Nos. 5,040,867; 5,261,020; 6,816,661; and 6,931,193. In particular, U.S. Pat. Nos. 6,816,661 and 6,931,193 describe a UNICAM® installation tool available from Corning Cable Systems LLC of Hickory, N.C. designed specifically to facilitate mounting the UNICAM® family of fiber optic connectors upon the end portions of one or more field optical fibers. Such an installation tool 30 for mounting one or more field optical fibers 15 onto a single fiber or multifiber field-installable fiber optic connector 10 is shown in FIG. 2. In general, the installation tool 30 supports the mechanical splice connector 10, including the ferrule 12 and the splice components 17, 18, while the field optical fiber 15 is inserted into the connector and aligned with the stub optical fiber 14. In this regard, the installation tool 30 includes a tool base 32, a tool housing 34 positioned on the tool base, and an adapter 35 provided on the tool housing. The adapter 35 has a first end for engaging the mechanical splice connector 10 that is to be mounted upon the field optical fiber 15, and an opposed second end that serves as a temporary dust cap. The forward end of the mechanical splice connector 10 is received within the first end of the adapter 35, which in turn is positioned on the tool housing 34. The end portion of the field optical fiber 15 is then inserted and advanced into the open rear end of the mechanical splice connector 10 and the splice components 17, 18 are subsequently actuated, for example biased together by engagement of the cam member 20 with at least one of the splice components, in order to secure the stub optical fiber 14 and the field optical fiber 15 between the splice components. In the particular examples shown herein, the cam member 20 is actuated by rotating the cam actuator arm 36 provided on the tool housing 34 about ninety degrees (90°) around the longitudinal axis of the installation tool 30 and the mechanical splice connector 10 (i.e., compare the positions of the cam actuator arm 36 in FIG. 3A and FIG. 3B).
Once the fiber optic connector 10 is mounted upon the end portion of the field optical fiber 15, the resulting fiber optic cable assembly is typically tested end-to-end. Among other things, testing is conducted to determine whether the optical continuity established between the stub optical fiber 14 and the field optical fiber 15 is acceptable. While optical connections and fiber optic cables can be tested in many different manners, a widely accepted test involves the introduction of light having a predetermined intensity and/or wavelength into one of the stub optical fiber 14 or the field optical fiber 15. By measuring the light propagation through the fiber optic connector 10, and more particularly, by measuring the insertion loss and/or reflectance using an optical power meter or OTDR, the continuity of the optical coupling between the stub optical fiber 14 and the field optical fiber 15 can be determined. If testing indicates that the optical fibers are not sufficiently coupled (for example the end portion of the field optical fiber 15 and the end portion of the stub optical fiber 14 are not in physical contact or are not aligned) the operator must either scrap the entire fiber optic cable assembly or, more commonly, replace the fiber optic connector 10 in an attempt to establish the desired optical continuity. In order to replace the fiber optic connector 10, the operator typically removes (i.e., cuts) the fiber optic connector off the field optical fiber 15 and repeats the mechanical splice termination process described above utilizing a new mechanical splice connector on the installation tool 30 and mounting the new mechanical splice connector onto the end portion of the field optical fiber. Field-installable mechanical splice connectors have recently been developed that permit the splice termination to be reversed, and thereby avoid the need to scrap the entire fiber optic cable assembly or the fiber optic connector. Regardless, significant time and expense is still required to mount the fiber optic connector onto the field optical fiber, remove the cable assembly from the installation tool, conduct the continuity test and, in the event of an unacceptable splice termination, repeat the entire process.
In order to facilitate relatively simple, rapid and inexpensive continuity testing, Corning Cable Systems LLC of Hickory, N.C. has developed installation tools for field-installable mechanical splice connectors that permit continuity testing while the connector remains mounted on the installation tool. As previously described, the installation tool 30 includes an adapter 35 having opposed first and second ends, the first end of which is adapted to receive the mechanical splice connector 10. In order to test the continuity of the optical coupling between the field optical fiber 15 and the stub optical fiber 14, an optical power generator, such as a Helium-Neon (HeNe) gas laser 40, is provided to deliver a visible wavelength (e.g., red) laser light to the area within the fiber optic connector 10 where the end portion of the field optical fiber meets the end portion of the stub optical fiber, referred to herein as the “termination area.” In a particular embodiment, the visible light is delivered through the stub optical fiber 14 to the termination area via a test optical fiber 42 mounted upon a mating test connector 44 received within the second end of the adapter 35. As a result, the termination area is illuminated with visible light that produces a “glow” indicative of the amount of light from the stub optical fiber 14 being coupled into the field optical fiber 15. At least a portion of the connector 10 is formed of a transparent or non-opaque (e.g., translucent) material, for example the splice components 17, 18 and/or the cam member 20, so that the glow at the termination area is visible to the operator.
By monitoring the dissipation of the glow emanating from the termination area (i.e., from the stub optical fiber 14) before and after the field optical fiber 15 is inserted into the fiber optic connector 10 and terminated, the operator can determine whether there is sufficient physical contact and/or alignment between the field optical fiber 15 and the stub optical fiber. In particular, continuity of the optical coupling between the field optical fiber 15 and the stub optical fiber 14 is presumed to be established if the initial glow dissipates below a threshold amount. In instances when the splice termination is unacceptable (i.e., the initial glow emanating from the termination area does not dissipate below the threshold amount), the field optical fiber 15 may be repositioned relative to the stub optical fiber 14 and terminated again to the fiber optic connector 10 until the splice termination is acceptable. As previously mentioned, the installation tool 30 may be configured to permit the cam member 20 to be un-actuated (i.e., reversed) in the event that the splice termination is unacceptable (i.e., the glow emanating from the termination area is greater than the threshold amount), thereby releasing the splice components 17, 18, so that the field optical fiber 15 can be repositioned relative to the stub optical fiber 14 and again terminated to the fiber optic connector 10. However, the operator should not attempt to cause the glow to dissipate prior to actuating the cam member 20 by moving the field optical fiber 15 around inside the connector 10 in an attempt to cause the glow to diminish prior to actuating the cam member. Moving the field optical fiber 15 can cause damage to the end portions of the field optical fiber and the stub optical fiber 14, and in particular to the fiber cleaves. The field optical fiber 15 should be inserted into the splice connector 10 and advanced until it makes physical contact with the stub optical fiber 14. When physical contact is made, the operator typically will see a flicker in the glow. When the cam member 20 is actuated, the glow should diminish significantly.
The Corning Cable Systems LLC method for verifying an acceptable splice termination described above is commonly referred to as the “Continuity Test System” (CTS) and the combined functionality of the visible light laser 40, test optical fiber 42 and test connector 44 are commonly referred to as a “Visual Fault Locator” (VFL). In practice the method is generally sufficient for determining whether the majority of splice terminations are acceptable since the quality of the splice need not be maintained to a high degree of precision and the operator is typically highly-trained and experienced. However, in certain circumstances, for example when a fiber optic network requires an exceptionally low insertion loss, it is important to maintain the quality of the splice termination to a greater degree of precision. At the same time, it is desirable to utilize less highly-trained and experienced operators in order to reduce the overall cost of installing a fiber optic network. In such situations, a potential shortcoming of the above-described CTS method using a VFL is the variability of the amount of glow emanating from the termination area before and after the field optical fiber 15 is terminated to the splice connector 10. In particular, it may be difficult even for a highly-trained and experienced operator to assess whether the change in the amount of glow emanating from the termination area is substantial enough to indicate an acceptable splice termination. Variations in the ambient light, variations in the translucence of different fiber optic connectors, the operating condition of the VFL and the adapter, the subjectivity of the operator, and the variability introduced by different operators conducting the same test for different splice terminations are just some of the factors that contribute to the varying and inconsistent results that may be obtained when conducting continuity testing using a VFL.
Furthermore, depending upon the translucence of the fiber optic connector and the intensity of the visible laser light, the termination area may continue to glow appreciably (sometimes termed “nuisance glow”) even after an acceptable splice termination. As a result, a less highly-trained and experienced operator may attempt multiple insertions of the field optical fiber and/or splice terminations using the same fiber optic connector in an effort to further diminish or entirely eliminate the nuisance glow in an acceptable splice termination. These misguided efforts of the untrained or inexperienced operator typically cause damage to the fiber optic connector or to the field optical fiber, or result in optical performance that is less than that which would have been achieved had the operator accepted the first termination, even though the glow was not completely diminished and the nuisance glow persisted. Contrary to common understanding, it is the difference in the visible amount of glow emanating from the termination area before and after the field optical fiber is terminated rather than the residual amount of glow that is most critical in determining whether a particular splice termination is acceptable. Accordingly, improved apparatus and methods are needed to reduce the overall time and cost required to obtain an acceptable splice termination. Improved apparatus and methods are also needed to eliminate the subjectivity presently introduced by an operator when verifying an acceptable splice termination in a field-installable fiber optic connector, and to thereby correspondingly increase the accuracy of determining whether a particular splice termination is acceptable. Preferably, such apparatus and methods should accommodate existing installation tools for field-installable fiber optic connectors, and more preferably, existing installation tools for single fiber and multifiber field-installable mechanical splice connectors.
Additional features and advantages of the invention are set forth in the detailed description which follows and will be readily apparent to those skilled in the art from that description, or will be readily recognized by practicing the invention as described in the detailed description, the drawings and the appended claims. It is to be understood that both the foregoing general description and the following detailed description present exemplary embodiments of the invention as well as certain preferred embodiments. As such, the detailed description is intended to provide an overview or framework for understanding the nature and character of the invention as recited in the appended claims. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated into and constitute a part of this specification. The drawings illustrate various preferred embodiments of the invention, and together with the detailed description, serve to explain the principles and operations thereof. Additionally, the drawings and descriptions are meant to be merely illustrative, and are not intended to limit the scope of the claims in any manner.